1. Field of the Technique
This invention relates to a pressure converter adapted to convert pressure into an electric signal.
2. Prior Art
There have been proposed and practically employed a variety of pressure converters adapted to convert various pressures to be applied to pistons of internal combustion engines in automobiles such as oil, air, coolant pressures and pressures for air conditioning, for example, into any form such as electric signals, for example.
One prior art pressure converter is illustrated and described in Japanese Laid-Open Utility Model Application No. 205,042/82. The prior art pressure converter generally comprises a cap having a center pressure inlet; a main body partially covered by the cap and having a vertically extending center through opening, a contoured upper surface and a downwardly extending reduced diameter cylindrical portion, said cylindrical portion being formed in the side wall with a vertical notch; a diaphragm pinched between the undersurface of the cap and the contoured upper surface of the main body; a piston received within the cylindrical portion of the main body for vertical movement; a piston rod connected to and extending upwardly from the piston through the center through opening in the main body and having an integral center disc at the upper end of the rod; a potentiometer mounted on the outer surface of the main body cylindrical portion; a lever pivoted to the potentiometer for vertical movement and connected to the piston through the vertical notch; a lower member connected to the lower end of the main body and having an external terminal extending downwardly from the lower member and connected to the potentiometer; a return spring received within the lower member to normally bias the piston upwardly; and an adjusting rod contacting the spring to adjust the biasing force of the spring.
As the pressure within the chamber defined between the inner surface of the cap and the upper surface of the diaphragm increases by allowing pressure to flow axially into the chamber through the pressure inlet in the cap, when the pressure within the chamber overcomes a force which is the product of the force of the return spring, the effective pressure receiving area of the diaphragm and the introduced pressure, the diaphragm is depressed down together with the piston rod end disc which in turn pushes the piston down deep into the cylindrical portion of the main body to thereby push the lever engaging in the piston downwardly.
As the piston moves downwardly under the increased pressure within the chamber as mentioned hereinabove, the lever associated with the potentiometer follows the downward movement of the piston and as a result, the resistance value within the potentiometer varies. That is, the linear movement of the diaphragm is not required to be converted into a rotational movement because the potentiometer is not a rotary type, but a linear slide type.
However, in the pressure converter described just above, since the piston adapted to receive pressure is biased by the return spring, when subjected to pressure, the piston moves downwardly frictionally in the axial direction against the force of the return spring and thus, frictional resistance produces between the piston and spring to cause loss of pressure. Therefore, when the pressure is converted into an electric signal, the electric signal fails to represent the net value of the applied pressure.